First gold is not the best conductor, silver than copper. Gold is used because it does not oxidize as quickly as other metals, but has nothing to do with sound quality.
There are differences in the sound and video quality of cables and HDMI cables, but its not because of gold, its because of the materials used in the cable, the type and size of the conductors, how its stranded, the dielectric that surrounds the conductors etc.
40 years high end audio video specialist
Edit: I have to make a comment about something that everyone gets wrong about digital. Digital is not just digital and many people say it makes no difference, so just get the cheapest. This is not true at all ! There is a difference in the quality of the digital signal and transmission of that signal and the cable does have a big effect on this. Sure most people the cheap cable is good, but for those wanting to get the best possible picture and sound, you definitely want to invest in higher end digital cables, including HDMI cables. The thing is the chain stores do not sell better cables worth the investment, you must go to your local independent high end audio video store to buy them. They carry the better brands worth the investment. But don't let anyone tell you it makes no difference because its a digital signal.